Update Tinify SDK

[tijmenbruggeman]

We've update the dev-create-key branch in tinify/tinify-php#38. To update the WordPress plug-in to this version as well we need to update the composer package.

Changes

• Remove facebook/webdriver. This was used for the previous integration tests. The package is abanonded since 2020 (https://packagist.org/packages/facebook/webdriver)
• Remove symfony/yaml is no longer used
• Update lock, this will update the PHP SDK for Tinify which causes the code changes as we save it in the plug-in.